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60 cycle subwoofer hum elusive ground

I have a Vandersteen powered subwoofer with a constant 60 cycle hum. I might have a grounding problem because we have a 50 year old house with the 2 prong outlets. Is there a way to defeat this humming under these circumstances? I've tried "grounding" to the outlet using the mounting screw and this only somewhat quieted it more than the connection that I ran from the sub grounding screw to the shielded portion of the speaker wire. I tried running a long wire from the ground connection to a light switch and this made it worse, almost like this wire was acting as an antenna to surrounding RF from the house wiring. The main speakers are Martin Logan's and are also powered; these are quiet. Any suggestions would be appreciated.

I have to ask why you would be running such nice gear on ungrounded old wiring like that. You should at least be running everything through a power conditioner. Make sure your source and the sub are connected to the same outlet if possible. Might help eliminate the ground loop.

Thanks. I forgot to mention that we upgraded our house service about 4 years ago during which installation I had a lightning arrestor and surge protector added to the main power box. We also had the wiring which serves the wall with the audio equipment (amp, receiver, front and center speakers, etc) upgraded to a grounded wiring system going all the way to the new house service. The sub, however, is plugged in on the other 50 year old side of the room. We also have a power conditioner that all components plug into. With this in mind shouldn't the ground be carried to the sub via the shielded audio cable connected to it? My main speakers accommodate low base pretty well so I didn't feel too bad removing the the sub from the system about 4 years ago but I would like to solve this problem so I can reconnect it. Thanks again and sorry for the long post.

I haven't tried a ground loop transformer but will tomorrow when Radio Shack opens. As far as grounding to plumbing goes, the equipment is far removed from a way to do that but if the ground loop protector doesn't solve the problem I will at least test that approach with a long extension cord. I'll post results of this experiment.

I haven't tried a ground loop transformer but will tomorrow when Radio Shack opens. As far as grounding to plumbing goes, the equipment is far removed from a way to do that but if the ground loop protector doesn't solve the problem I will at least test that approach with a long extension cord. I'll post results of this experiment.

They work wonders... I use them a lot in Car Audio, especially with things like Sirius/XM that loves to use 5V, which means the ground will never (ever!) be on the same plane.

First you want all equiptment grounded to the same point, that's usually the best thing. If that doesn't work, the Ground Loop.

The Third thing is what we call a "ground lift", but I won't explain that as I don't recommend it unless you know what you are doing... and 99% of the time the Ground Loop Isolator does a good enough job without causing a safety issue.

Thanks again. I haven't gotten to the ground loop trial yet, but I need to mention one more thing. In order to use the sub at all, I reduced the hum by connecting the ground terminal on the sub to the shielding on the audio cable. Without doing this the hum is so loud that one couldn't carry on a conversation in the same room. If I disconnect the audio cable, the hum is unchanged.

I have four ground loop iso's that I got from RadioShack between my computers and my 9.2 and they work great. My reason is that I am on the same circuit, but two different outlets on different ends of the room and it wants to mess with the I/O of my systems.

Also if your receiver has the ability to attach a turntable, there should also be a ground lug for it that you can try. I have done this in the past and it worked great.